Nanometer-scale studies of vertical organization and evolution of stacked self-assembled InAs/GaAs quantum dots

We have investigated the vertical organization and evolution of 1-, 5-, 10- , and 20-layer stacks of molecular beam epitaxially grown self-assembled In As/GaAs quantum dots using high resolution and large-scale cross-sectional scanning tunneling microscopy. We report results regarding the evolution of the dot sizes and shapes, and the assembly of vertically organized columns of stacked dots. As the number of dot layers within a stack is increased, the average spacing between vertically organized columns decreases, and the corresponding dots become more uniform in size. The data also suggest that the coalescence of neighboring stacks of dots has not occurred and therefo re coalescence is not the mechanism leading to the observed uniform distrib ution of dot sizes and column spacings. (C) 1999 American Institute of Phys ics. [S0003-6951(99)02619-4].